Project Background & Challenges

Officially opened in 1965 just 25 miles north of Pittsburgh, the wastewater treatment plant at Seneca Landfill has the capacity to store millions of gallons of water and process up to 110,000 gallons per day. In order to treat and clean the water, it uses a multi-stage treatment system to process contaminated water from the landfill, so that it can be released safely back into Connoquenessing Creek without any negative impact on wildlife or human populations.

The sources for this water are condensate and deliquification water, which are both produced only during gas pumping, as well as leachate, which includes sources like rainwater that may meet waste from the landfill and become contaminated. By 2010, modifications and continued studies on environmental impact showed the amount of ammonia in the wastewater from these sources was proving to be too much for the existing system.

The original system at Seneca Landfill consisted of three bio-towers, filled with outdated trickling filter media. At the time, only two were in operation – all of which contributed to the system being unable to reduce effluent ammonia to required levels.

The Nexom Answer

After studying the various options available, engineers from Bassett Engineering worked with the team from Seneca Landfill to create a plan that that would convert their existing but outdated Bio-Towers to a BioPorts™ Moving Bed Biofilm Reactor (MBBR), which would eventually run in a series.

The bio-towers would be updated one at a time with new BioPort media, which also provided an opportunity to measure effluent characteristics at three different intermediate flow configurations along the way, in addition to the final reactor configuration.

Ammonia Management Issues

Landfill leachate is a common waste type characterized by extremely high BOD and ammonia spikes. While the average ammonia level in the influent is 1,400 mg/L, Seneca Landfill has historically reported days where the influent has been as high as 3,372 mg/L, and on occasion, as high as 5,000 mg/L. In keeping with their permit limit, Seneca Landfill needed to obtain an onsite ammonia effluent limit of less than 4.7 mg/L and was not consistently able to meet that target using their own system, thereby forcing them to incur additional costs for off-site treatment.

Part of the cause of these high ammonia levels was the decision of the landfill owners to extract the methane gas being produced by the landfill. When organic matter ends up in a landfill, it breaks down over time, generating gases like methane. Traditionally, landfills use flares to burn off both excess methane and CO₂. Instead, Seneca Landfill chose to capture the methane and convert it into a clean form of natural gas for future use – with one of those uses being to help power the landfill itself. However, the methane extraction process produces condensate, a wastewater with an even higher concentration of ammonia than the original landfill leachate, and this rendered the existing wastewater treatment system insufficient.

Design Flow

Leachate from the Seneca Landfill is first collected in two equalization tanks, which allows operators to control the flow rate from the equalization tanks to the system, and from there is pumped through the metals removal system. Metals removal is accomplished by the addition of sodium hydroxide (caustic) as well as ferric chloride. Next, the wastewater is sent to a sludge separator for primary sludge removal and is heated to help facilitate ammonia removal as well as to maintain consistency for the biomass in the reactors.

Wastewater enters the fully aerated tank and encounters the biofilm-coated media. Coarse effluent screens are also installed to prevent the patented BioPorts™ media from leaving the tank. Depending on the configuration, multiple tanks in the series can be used to meet low effluent requirements and/or address several different contaminants and nutrients.

Site Construction

The retrofit of the first bio-tower to a BioPorts™ MBBR reactor was completed in September 2011. By updating the towers one at a time, this ensured minimal disruption and downtime for the landfill. It also provided an opportunity to measure effluent characteristics at three different intermediate flow configurations along the way, in addition to the final reactor configuration.

The project was completed over the course of six months, with the third BioPorts reactor coming online in June 2012. The final configuration consisted of wastewater from the landfill flowing through the three upgraded BioPorts MBBR reactors in a series.

Upgraded System Performance

The average influent flow rate the Seneca Landfill towers experienced from September 2011 through June 2012 was 18.1 GPM, or 26,000 GPD. This new system is designed to achieve effluent ammonia concentrations of 4.7 mg/L and is consistently able to achieve this limit or less, therefore enabling them to discharge their wastewater into Connoquenessing Creek.

After the updated BioPorts MBBR reactors were put in place, the landfill was able to achieve its objective of converting landfill gases, specifically methane, into enough green energy to power not only a third of the landfill’s daily operations, but also to heat over 27,000 homes in western Pennsylvania. It also supplies compressed natural gas for fueling CNG vehicles (including the landfill’s own fleet).